Fix visit() promise resolution

[krisselden]

The fix in this PR makes the issue worse, it is now less likely render is fully resolved when the visit promise is resolved.

#14591

This issue causes a lot of tests to force flush the run loop to ensure visit is done rendering.

To clarify, this issue isn't about error handling, it is about actually resolving the promise only when rendering is actually settled.

[tomdale]

@krisselden Can you provide some more context about this bug?

The fix in this PR makes the issue worse, it is now less likely render is fully resolved when the visit promise is resolved.

What does "it" refer to here?

What are the specific behaviors that we need to change about the current implementation for us to consider promise resolution fixed and close this bug?

[krisselden]

that the promise resolves here https://github.com/emberjs/ember.js/blob/master/packages/ember-glimmer/lib/renderer.ts#L194

[krisselden]

Also, I think it would be nice to have an API for a promise when rendering has settled.

[rwjblue]

As a mechanism to flush out tests that artificially forced visit to behave synchronously, I swapped Ember.ApplicationInstance.prototype.visit out to use run.next instead of run.schedule('afterRender', ....) (temporarily) and then fixed all the test failures. That work is progressing in #16086.